1. Field of the Invention
The present invention relates to a method of and apparatus for producing a product with a coating layer in a mold.
2. BACKGROUND OF THE INVENTION
To provide plastic products molded from what is called a "sheet molding compound" (SMC), such as thermosetting plastic sheet materials, without any surface defects such as convexity or pin holes, it is known to apply a coating either fully or partly to the surface of the molded plastic product in a mold by in-mold coating.
Typically, in an in-mold coating method, a molded product is produced by applying a desired mold die pressure to upper and lower mold dies between which a mold cavity is formed to hold plastic material filled therein. After being impregnated into the cavity with high pressure to cover the surface of the molded product, fluidized plastic material, such as polyester or urethane, is thermoset to form a coating layer. When impregnating the fluidized plastic material in the cavity, the mold cavity pressure applied to the upper and lower dies is rapidly reduced. Such an in-mold coating method is known from, for instance, U.S. Pat. No. 4,668,460, entitled "METHOD OF MOLDING AND COATING A SUBSTRATE IN A MOLD," patented May 26, 1987.
Because of such a rapid reduction in mold cavity pressure, the molded product in the cavity may have a non-uniform density distribution produced over its surface, so as to sticks and digs, resulting in a lack of a precisely smooth surface on the molded product. It is difficult to prevent fluidized plastic material of coating layers for such molded products from sticking and digging on the finish.
The smoothness of the fluidized plastic material of coating layer thermoset largely depends upon the mold cavity pressure upon when thermoset.